The present invention relates to a composition and method for permanent shaping of hair based on condensation products of cysteine and glycine.
Weakly acidic to neutral compositions for permanent shaping of hair are advantageously used for careful permanent shaping of damaged, especially white or dyed, hair. During the past 30 years thioglycolic acid esters have proven to be the best reducing agents for this purpose.
There are however a number of disadvantages opposing the advantages provided by a permanent shaping treatment of hair performed with a weakly acidic to neutral permanent shaping composition. Permanent shaping compositions based on thioglycolic acid esters have reduced waveability in comparison to mild alkali shaping agents based on thicoglycolate. For this reason heat, a lengthening of the treatment time to 20 to 60 minutes and the use of comparatively thin curlers are required. Use of this permanent shaping agent for normal, undamaged natural hair is not accepted or meaningful, because of the longer required treatment time of over 30 minutes and the required heat, so that the use of weakly acidic to neutral permanent shaping compositions has up to now usually been limited to pre-damaged, easily worked hair.
An additional considerable disadvantage of acidic permanent shaping compositions is the poor eye and skin compatibility and the sensitizing action of thioglycolic acid esters.
Inspite of a number of attempts the current Sensitizing effects of acidic permanent shaping compositions have not been decisively reduced.
A mildly alkaline (pH=7.1 to 9) permanent shaping composition, which contains cysteine or its salts as active keratin-reducing agents, has been suggested as an alternative.
This hair shaping agent however has a similar series of disadvantages. Cysteine provides only a weak hair shaping effect and has a reduced stability. When cysteine-containing permanent shaping agents are applied to the hair, the cysteine is oxidized quickly by the oxygen in the air to the weakly soluble cystine in water, which forms a difficult-to-remove white coating which is deposited on the hair (so-called "whitening effect").
There have already been a number of attempts to avoid this "whitening effect". They usually include addition of a coreducing agent, or another compound which reduces the oxidizability of cysteine, to hair shaping compositions based on cysteine to solve this problem. The "whitening effect" however could not be eliminated to a satisfactory extent with these steps. Furthermore the current hair shaping compositions including these features have an insufficient hair shaping effect or an unacceptable potential for causing allergic reactions.